U.S. patent number 10,029,205 [Application Number 15/258,076] was granted by the patent office on 2018-07-24 for two stage adsorbent and process cycle for fluid separations.
This patent grant is currently assigned to EXXONMOBIL RESEARCH AND ENGINEERING COMPANY. The grantee listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Narasimhan Sundaram, Hans Thomann.
United States Patent |
10,029,205 |
Sundaram , et al. |
July 24, 2018 |
Two stage adsorbent and process cycle for fluid separations
Abstract
In various aspects, apparatuses, systems, and methods are
provided for performing two stage separation of CO2 from a gaseous
stream. The first stage adsorbent can be comprised of a plurality
of cylindrical or substantially cylindrical rings. The first stage
adsorbent can be comprised of a metal organic framework. The second
stage adsorbent can be subject to a displacement desorption
process. The second stage adsorbent can be comprised of a support
and a metal compound selected from the group consisting of alkali
or alkaline earth. The first and second stage adsorbent can be
arranged concentrically for space and efficiency
considerations.
Inventors: |
Sundaram; Narasimhan
(Annandale, NJ), Thomann; Hans (Bedminster, NJ) |
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
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Assignee: |
EXXONMOBIL RESEARCH AND ENGINEERING
COMPANY (Annandale, NJ)
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Family
ID: |
57045391 |
Appl.
No.: |
15/258,076 |
Filed: |
September 7, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170087503 A1 |
Mar 30, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62232705 |
Sep 25, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D
53/0462 (20130101); B01J 20/3425 (20130101); B01D
53/0407 (20130101); B01J 20/3458 (20130101); B01D
53/0431 (20130101); B01D 53/0446 (20130101); B01J
20/226 (20130101); B01D 2253/204 (20130101); B01D
2253/25 (20130101); B01D 2259/4009 (20130101); B01J
20/04 (20130101); B01D 2259/414 (20130101); Y02C
20/40 (20200801); B01D 2257/504 (20130101) |
Current International
Class: |
B01D
53/04 (20060101); B01J 20/04 (20060101) |
Field of
Search: |
;95/139,148
;96/132,154 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
McDonald et al., "Cooperative Insertion of CO2 in Diamine Appended
Metal-Organic Frameworks", Nature, Mar. 19, 2015, pp. 303-308, vol.
519, Nature.com. cited by applicant .
McDonald et al., "Capture of Carbon Dioxide From Air and Flue Gas
in the Alkylamine-Appended Metal-Organic Framework
mmem-Mg2(dobpdc)", Journal of the American Chemical Society, Apr.
4, 2012, pp. 7056-7065, vol. 134, iss. 16, ACS Publications. cited
by applicant .
PCT/US2016/050505 International Search Report and Written Opinion
dated Jan. 20, 2017. cited by applicant .
Wilcox, "Chapter 4: Adsorption Table 4.6", Carbon Capture, 2012, p.
160, Springer-Verlag New York. cited by applicant.
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Primary Examiner: Lawrence; Frank
Attorney, Agent or Firm: Ward; Andrew T.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application
Ser. No. 62/232,705 filed on Sep. 25, 2015, herein incorporated by
reference in its entirety.
Claims
What is claimed is:
1. A method for separation of CO.sub.2 from a gaseous stream,
comprising contacting the gaseous stream with a first stage steam
sensitive adsorbent such that CO.sub.2 is adsorbed into the first
stage adsorbent and a first CO.sub.2-lean stream is formed;
desorbing CO.sub.2 from the first stage adsorbent thereby forming a
first CO.sub.2-rich stream; contacting the first CO.sub.2-rich
stream with a second stage steam insensitive adsorbent such that
CO.sub.2 is adsorbed in the second stage adsorbent and a second
CO.sub.2-lean stream is formed; and desorbing CO.sub.2 from the
second stage adsorbent thereby forming a second CO.sub.2-rich
stream; wherein the second CO.sub.2-rich stream has a higher
CO.sub.2 concentration by mol. % than the first CO.sub.2-rich
stream.
2. The method of claim 1, wherein the first stage adsorbent
consists of a metal organic framework.
3. The method of claim 1, wherein the second stage adsorbent
comprises a support and a metal compound selected from the group
consisting of alkali or alkaline earth.
4. The method of claim 1, wherein the contacting the gaseous stream
and the desorbing CO.sub.2 from the first stage adsorbent steps are
performed using a temperature swing process.
5. The method of claim 1, wherein the contacting the first
CO.sub.2-rich stream and the desorbing CO.sub.2 from the second
stage adsorbent steps are performed using a displacement
process.
6. The method of claim 1, wherein the pressure of the gaseous
stream is less than 2 bar.
7. The method of claim 1, wherein the temperature of the gaseous
stream is between about 60.degree. C. and 90.degree. C.
8. The method of claim 4, wherein the temperature swing process
comprises, contacting the gaseous stream with the first stage
adsorbent at a first temperature, said first temperature being less
than an adsorption temperature of CO.sub.2 for the first stage
adsorbent, heating the first stage adsorbent with a hot purge gas,
wherein the hot purge gas is at a second temperature, said second
temperature being greater than a desorption temperature of CO.sub.2
for the first stage adsorbent.
9. The method of claim 8, wherein the hot purge gas comprises
N.sub.2.
10. The method of claim 8, wherein the hot purge gas comprises
N.sub.2 and CO.sub.2.
11. The method of claim 8, wherein the hot purge gas comprises
flare gas.
12. The method of claim 8, wherein the first stage adsorbent is
heated by the hot purge gas by indirect heat exchange.
13. The method of claim 8, wherein the temperature differential
between the first temperature and the second temperature is less
than 90.degree. C.
14. The method of claim 8, wherein the temperature differential
between the first temperature and the second temperature is less
than 70.degree. C.
15. The method of claim 8, wherein the temperature differential
between the first temperature and the second temperature is less
than 50.degree. C.
16. The method of claim 8, wherein the temperature differential
between the first temperature and the second temperature is less
than 30.degree. C.
17. The method of claim 5, wherein the displacement process
comprises, contacting the first CO.sub.2-rich stream with the
second stage adsorbent such that CO.sub.2 is adsorbed into the
second stage adsorbent; and contacting the second stage adsorbent
with steam such that CO.sub.2 is desorbed from the second stage
adsorbent.
18. The method of claim 17, wherein CO.sub.2 is desorbed from the
second stage adsorbent via one or both of concentration swing and
displacement desorption.
19. The method of claim 17, wherein the displacement process is
conducted at an initial temperature; wherein the initial
temperature does not vary more than 10.degree. C. during the
contacting the first CO.sub.2-rich stream with the second stage
adsorbent and the contacting the second stage adsorbent with steam
steps.
20. The method of claim 5, wherein the contacting the first
CO.sub.2-rich stream and the desorbing CO.sub.2 from the second
stage adsorbent steps are performed using a displacement process;
wherein the displacement process comprises, contacting the first
CO.sub.2-rich stream with the second stage adsorbent such that
CO.sub.2 is adsorbed into the second stage adsorbent; contacting
the second stage adsorbent with steam such that CO.sub.2 is
desorbed from the second stage adsorbent.
21. The method of claim 20, wherein the steam usage in moles to
CO.sub.2 desorbed in moles ratios is less than 3.
22. The method of claim 1, wherein the first the first stage
adsorbent is disposed radially about a central axis; wherein the
first stage adsorbent has an interior surface that is a distance x
from the central axis and an exterior surface that is a distance y
from the central axis, wherein y is greater than x, thereby forming
a void space between the central axis and the interior surface of
the first stage adsorbent.
23. The method of claim 22, wherein the second stage adsorbent is
disposed within the void space of the second stage adsorbent.
24. The method of claim 20, wherein the heat of condensation from
the CO.sub.2 that is desorbed from the second stage adsorbent is
used to heat the gaseous stream.
25. The method of claim 1, wherein the CO.sub.2 content in the
gaseous stream is about 3-10 mol. %.
26. The method of claim 1, wherein the CO.sub.2 content in the
first CO.sub.2-rich stream is about 20-35 mol. %.
Description
FIELD
Systems and methods are provided for improving the efficiency of
adsorbents during adsorption processes.
BACKGROUND
Gas separation is important in many industries and can typically be
accomplished by flowing a mixture of gases over an adsorbent that
preferentially adsorbs a more readily adsorbed component relative
to a less readily adsorbed component of the mixture. Fossil fuels
currently supply the majority of the world's energy needs and their
combustion is the largest source of anthropogenic carbon dioxide
emissions. Carbon dioxide is a greenhouse gas and is believed to
contribute to global climate change. Concern over global climate
warming has led to interest in capturing CO.sub.2 emissions from
the combustion of fossil fuels. CO.sub.2 can be removed from
combustion flue gas streams by varying methods.
Combustion gases vary in composition depending on the fuel and the
conditions of combustion. The combustion gases can be produced in
furnaces and in gas turbines, including the combustion gases
produced in the generation of electric power. The fuels used are
predominantly coal and natural gas. Coal is burned in furnaces,
while natural gas is burned both in furnaces and in gas turbines,
but in electric power generation natural gas is mainly burned in
gas turbines.
The quantities of combustion gas produced in electric power
generation are very large because of the scale of furnaces and
turbines used. One measure of the scale of these operations is the
amount of CO.sub.2 produced in a typical 500 Megawatt power plant.
For coal fired power generation, the rate of CO.sub.2 production is
on the order of 100 kilograms per second; for gas fired power
production it is more like 50 kilograms per second.
The challenge for flue gas CO.sub.2 capture is to do it efficiently
to minimize the cost. All post-combustion CO.sub.2 capture
technologies suffer from the disadvantage that the CO.sub.2 in the
flue gas is present at low pressure (just about 1 atm) and in low
concentrations (3 to 15%). A large amount of energy is needed to
separate the CO.sub.2. For 90% recovery of 10% CO.sub.2 in a flue
gas at 1 atm, the CO.sub.2 must be brought from 0.1 atm to 1 atm,
and then further compressed to a delivery pressure of 150 atm.
Analyses conducted at NETL shows that CO.sub.2 capture and
compression using a conventional absorption process raises the cost
of electricity from a newly built supercritical PC power plant by
86%, from 64 cents/kWh to 118.8 cents/kWh (Julianne M. Klara,
DOE/NETL-2007/1281, Revision 1, August 2007, Exhibit 4-48 LCOE for
PC Cases). Aqueous amines are considered a state-of-the-art
technology for CO.sub.2 capture for PC power plants, but have a
cost of $68/ton of CO.sub.2 avoided) (Klara 2007,
DOE/NETL-2007/1282). Developing methods that minimize the amount of
energy and other costs will be necessary if CO.sub.2 removal from
flue gas is to be economical.
Methods for the removal of CO.sub.2 from gas streams, include
adsorption with a solvent, adsorption with a sorbent, membrane
separation, and cryogenic fractionation and combinations thereof.
In absorption/desorption processes to capture CO.sub.2, the energy
needed to regenerate the sorbent or solvent is a large cost
element.
One of the more important gas separation techniques is temperature
swing adsorption (TSA). TSA processes also rely on the fact that
under pressure gases tend to be adsorbed within the pore structure
of the microporous adsorbent materials or within the free volume of
a polymeric material. When the temperature of the adsorbent is
increased, the adsorbed gas is released, or desorbed. By cyclically
swinging the temperature of adsorbent beds, TSA processes can be
used to separate gases in a mixture when used with an adsorbent
that is selective for one or more of the components in a gas
mixture. TSA processes are generally preferred when the adsorbate
concentration in the feed is less than 10%, although TSA processes
can be used at greater percentages. See Jennifer Wilcox, CARBON
CAPTURE, Table 4.6, 160 (Springer 2012).
Another important gas separation technique is known as a
displacement purge or displacement desorption ("DD"). In the DD
cycle the displacement purge fluid in the regeneration step adsorbs
nearly as strongly as the adsorbate so that desorption is favored
by both change in partial pressure and competitive adsorption
through the displacement of surface-bound CO.sub.2. Typical cycle
times are on the order of several minutes. In this process since
the heat of adsorption of the displacement purge fluid, normally
steam, is approximately equal to that of the adsorbate, the net
heat generated or consumed is essentially negligible, maintaining
nearly isothermal conditions throughout the process, which allows
for higher sorbent loading compared to an inert-purge process. DD
processes are generally preferred when the adsorbate concentration
in the feed is greater than 10%, although DD processes are used at
lesser percentages. See Jennifer Wilcox, CARBON CAPTURE, Table 4.6,
160 (Springer 2012).
Conventional swing adsorption processes suffer a variety of
drawbacks. Specifically, in both TSA and DD processes, the ratio of
steam required to the amount of CO.sub.2 recovered is oftentimes at
an economically inefficient/unacceptable level, e.g. between 3 to
10 moles of steam usage per mole of CO.sub.2 recovered. There is a
need for energy efficient removal of carbon dioxide from low
pressure flue gas with existing adsorbents.
U.S. Pat. No. 8,900,347 describes a temperature swing adsorption
apparatus. The apparatus includes axial thermally conductive
filaments that can assist with heating and/or cooling of the
adsorbent.
U.S. Pat. No. 8,784,533 describes a temperature and/or pressure
swing adsorption process using a solid adsorbent, such as an
adsorbent provided as a parallel channel contactor. The temperature
of the solid adsorbent can be controlled by introducing a heating
and/or cooling fluid through heating and/or cooling channels in the
adsorbent that are not in fluid communication with the channels
that provide the feed gas for separation. This can allow physical
contact between the heating and/or cooling fluid without exposing
the gas being separated to the fluid.
U.S. Publication No. 2015/0008366 A1 describes a displacement
process an essentially isothermal cyclic adsorption process, and is
incorporated herein by reference in its entirety. A driving force
for adsorption and desorption/regeneration of the CO.sub.2 can be a
combination of concentration swing and desorptive
displacement/adsorption. During adsorption, incoming CO.sub.2
molecules adsorb onto the sorbent and also displace previously
adsorbed water (adsorptive displacement or displacement
adsorption), during which time the water also desorbs by
concentration swing. During desorption/regeneration, the water
molecules from the steam adsorb onto the adsorbent and displace the
CO.sub.2 (desorptive displacement or displacement desorption). The
DD process utilizes an adsorbent composed of a support and a metal
compound selected from the group consisting of alkali and alkaline
earth.
Thomas M. McDonald et al., Cooperative Insertion of CO.sub.2 In
Diamine-Appended Metal-Organic Frameworks, 519 NATURE 303 (2015)
and Thomas M. McDonald et al., Capture of Carbon Dioxide From Air
and Flue Gas In the Alkylamine-Appended Metal-Organic Framework
mmem-Mg.sub.2(dobpdc), 134 J. AM. CHEM. SOC. 7056 (2012) describe
the use of metal organic frameworks (MOFs) in temperature swing
adsorption processes.
SUMMARY
In various aspects, apparatuses, systems, and methods are provided
for performing two stage separation of CO.sub.2 from a gaseous
stream. In one aspect, a first stage adsorbent is provided. In
another aspect, the first stage absorbent can be comprised of a
plurality of cylindrical or substantially cylindrical rings. In the
context of this application, "substantially cylindrical" is
intended to include any type of prismatic shape, for example, a
polyhedron with two polygonal faces lying in parallel planes and
with the other faces being parellelograms. The first stage
adsorbent can be comprised of a MOF. In another aspect, a second
stage adsorbent is provided. The second stage adsorbent can be
subject to a DD process. The second stage adsorbent can be
comprised of a support and a metal compound selected from the group
consisting of alkali or alkaline earth.
In another aspect, the first stage adsorbent is disposed radially
about a central axis. In another aspect, the first stage adsorbent
has an interior surface that is a distance x from the central axis
and an exterior surface that is a distance y from the central axis,
wherein y is greater than x, thereby forming a void space between
the central axis and the interior surface of the first stage
adsorbent. In another aspect, the second stage adsorbent is
likewise disposed radially about a central axis. In another aspect,
the second stage adsorbent is disposed radially about the same
central axis of the first stage adsorbent. In another aspect, the
second stage adsorbent is disposed with the void space of the first
stage adsorbent.
In one aspect, a method for separation of CO.sub.2 from a gaseous
stream is provided. In another aspect, the method comprises
contacting the gaseous stream with a first stage steam sensitive
adsorbent such that CO.sub.2 is adsorbed into the first stage
adsorbent and a first CO.sub.2-lean stream is formed. In another
aspect, the method comprises desorbing CO.sub.2 from the first
stage adsorbent thereby forming a first CO.sub.2-rich stream. In
one aspect, the CO.sub.2 content of the gaseous stream is between
3-20 mol. %. In another aspect, the CO.sub.2 content of the first
CO.sub.2-rich stream is about 20-35 mol. %. In another aspect, the
method comprises contacting the first CO.sub.2-rich stream with a
second stage steam insensitive adsorbent such that CO.sub.2 is
adsorbed in the second stage adsorbent and a second CO.sub.2-lean
stream is formed. In another aspect, the method comprises desorbing
CO.sub.2 from the second stage adsorbent thereby forming a second
CO.sub.2-rich stream; wherein the second CO.sub.2-rich stream has a
higher CO.sub.2 concentration by mol. % than the first
CO.sub.2-rich stream.
In another aspect, the contacting the gaseous stream and the
desorbing CO.sub.2 from the first stage adsorbent steps are
performed using a TSA process. In another aspect, the temperature
swing process comprises contacting the gaseous stream with the
first stage adsorbent at a first temperature, said first
temperature being less than an adsorption temperature of CO.sub.2
for the first stage adsorbent, heating the first stage adsorbent
with a hot purge gas, wherein the hot purge gas is at a second
temperature, said second temperature being greater than a
desorption temperature of CO.sub.2 for the first stage adsorbent.
In another aspect of the TSA process the hot purge gas comprises
N.sub.2, CO.sub.2, or flare gas, such as methane. In another aspect
of the TSA process, the temperature differential between the first
temperature and the second temperature is less than 90.degree. C.,
less than 70.degree. C., less than 50.degree. C., less than
30.degree. C., or less than 20.degree. C. In another aspect, the
first stage adsorbent is heated by the hot purge gas by indirect
heat exchange.
In another aspect, the contacting the first CO.sub.2-rich stream
and the desorbing CO.sub.2 from the second stage adsorbent steps
are performed using a displacement process. In another aspect, the
displacement process comprises, contacting the first CO.sub.2-rich
stream with the second stage adsorbent such that CO.sub.2 is
adsorbed into the second stage adsorbent; and contacting the second
stage adsorbent with steam such that CO.sub.2 is desorbed from the
second stage adsorbent. In another aspect, CO.sub.2 is desorbed
from the second stage adsorbent via one or both of concentration
swing and displacement desorption. In another aspect, the
displacement process is conducted at an initial temperature;
wherein the initial temperature does not vary more than 10.degree.
C. during the contacting the first CO.sub.2-rich stream with the
second stage adsorbent and the contacting the second stage
adsorbent with steam steps.
In another aspect, the temperature swing process and displacement
process described above are used as the first and second stage
adsorption/desorption processes, respectively. In another aspect,
the ratio of steam usage in moles to CO.sub.2 desorbed in moles is
less than 3. In another aspect, the heat of condensation from the
CO.sub.2 that is desorbed from the second stage adsorbent is used
to heat the gaseous stream.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows an isometric view of an apparatus embodying aspects of
the current disclosure.
FIG. 2 shows a flow chart for a system embodying aspects of the
current disclosure.
FIG. 3 shows a graph of steam usage in moles as a function of
CO.sub.2 concentration.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Overview
As discussed above, both TSA and DD processes have shortcomings in
terms of steam usage required to achieve the level of CO.sub.2
separation that is required from gaseous streams. The term "steam
usage" is a term known to those skilled in the art. It does not
refer only to steam directly flowing over the adsorbent, but also
is used to describe steam used for any heating that is required
during adsorption processes. Indeed, many known adsorbents in
degrade if exposed to steam. If an adsorbent degrades in the
presence of steam, then it is said to be "steam sensitive." On the
other hand, if an adsorbent is "steam insensitive" then it is
understood to be able to generally withstand direct steam without
degradation of its adsorption characteristics. This is not to say
that a "steam insensitive" adsorbent would never degrade in the
presence of steam, but rather, would not degrade beyond that which
would be expected by a "steam sensitive" adsorbent under a purge
gas other than steam.
Temperature Swing Adsorption Processes
Swing adsorption processes can have an adsorption step in which a
feed mixture (typically in the gas phase) is flowed over an
adsorbent that can preferentially adsorb a more readily adsorbed
component relative to a less readily adsorbed component. A
component may be more readily adsorbed because of kinetic or
equilibrium properties of the adsorbent. The adsorbent is typically
contained in a contactor that is part of the swing adsorption unit.
In some aspects, a plurality of contactors can be used as part of a
swing adsorption system. This can allow adsorption and desorption
to be performed as a continuous process, with one or more
contactors being used for adsorption while one or more additional
contactors are used for desorption. As contactors approach maximum
loading during adsorption and/or approach complete desorption under
the desorption conditions, the flows to the contactors can be
switched between adsorption and desorption. It is noted that after
the desorption step, the adsorbent may retain a substantial loading
of the gas component. In various aspects, the loading of the
adsorbent with the adsorbed gas component at the end of the
desorption step can be at least about 0.1 mol/kg, or at least about
0.2 mol/kg, or at least about 0.5 mol/kg, or at least about 1.0
mol/kg, and/or about 3.0 mol/kg or less, or about 2.5 mol/kg or
less, or about 2.0 mol/kg or less, or about 1.5 mol/kg or less.
Additionally or alternately, the loading at the end of the
desorption step can be characterized relative to the loading at the
end of the prior adsorption step. The loading at the end of the
desorption step can be at least about 1% of the loading at the end
of the prior adsorption step, or at least about 10%, or at least
about 20%, or at least about 30%, or at least about 50%, and/or
about 70% or less, or about 60% or less, or about 50% or less, or
about 40% or less, or about 30% or less, or about 20% or less, or
about 10% or less.
The method of adsorbent regeneration designates the type of swing
adsorption process. Pressure swing adsorption (PSA) processes rely
on the fact that gases under pressure tend to be adsorbed within
the pore structure of the microporous adsorbent materials. The
higher the pressure, the greater the amount of targeted gas
component that will be adsorbed. When the pressure is reduced, the
adsorbed targeted component is released, or desorbed. PSA processes
can be used to separate gases of a gas mixture because different
gases tend to fill the micropore or free volume of the adsorbent to
different extents due to either the equilibrium or kinetic
properties of the adsorbent. TSA processes also rely on the fact
that gases under pressure tend to be adsorbed within the pore
structure of the microporous adsorbent materials. When the
temperature of the adsorbent is increased, the adsorbed gas is
released, or desorbed. By cyclically swinging the temperature of
adsorbent beds, TSA processes can be used to separate gases in a
mixture when used with an adsorbent that is selective for one or
more of the components in a gas mixture.
Temperature swing adsorption (TSA) processes, can employ an
adsorbent that is repeatedly cycled through at least two steps--an
adsorption step and a thermally assisted regeneration step.
Regeneration of the adsorbent can be achieved by heating the
adsorbent to an effective temperature to desorb target components
from the adsorbent. The adsorbent can then be cooled so that
another adsorption step can be completed. Such cooling may be
supplied by a cooling fluid either directly or indirectly. The
temperature swing adsorption process can be conducted with rapid
cycles, in which case they are referred to as rapid cycle
temperature swing adsorption (RCTSA). A rapid cycle thermal swing
adsorption process is defined as one in which the cycle time
between successive adsorption steps is less than about 10 minutes,
preferably less than about 2 minutes, for example less than about 1
minute. RC-TSA processes can be used to obtain very high product
recoveries in the excess of 90 vol %, for example greater than 95
vol % or, in some cases, greater than 98 vol %. The term
"adsorption" as used herein includes physisorption, chemisorption,
and condensation onto a solid support, absorption into a solid
supported liquid, chemisorption into a solid supported liquid, and
combinations thereof.
It is noted that a TSA cycle can also typically include a change in
the temperature of the adsorbent from the temperature for the
adsorption step to the temperature for the desorption step. The
adsorption step can be defined based on the time when the gas flow
is started for the input gas containing the component for
adsorption and when the gas flow is stopped. The desorption step
can be defined based on the time when gas being desorbed from the
adsorbent is collected to the time collection is stopped. Any time
in the cycle outside of those steps can be used for additional
adjustment of the adsorbent temperature.
A potential advantage of a TSA separation can be that the process
can be performed at a convenient pressure, or with a small amount
of variation around a convenient pressure. For example, a goal of a
TSA separation can be to develop a substantially pure stream of a
gas component that is adsorbed and then desorbed. In this type of
aspect, a convenient pressure for the desorption step can be a
temperature of about 1 bar (0.1 MPa) or less. Attempting to desorb
a stream at greater than about 0.1 MPa can require substantial
additional temperature increase for desorption. Additionally,
ambient pressure can be a convenient pressure for the adsorption
step as well, as many streams containing a gas component for
adsorption can correspond to "waste" or flue gas streams that may
be at low pressure. In some aspects, the pressure difference
between the adsorption and desorption steps can be about 1 MPa or
less, or about 0.2 MPa or less, or about 0.1 MPa or less, or about
0.05 MPa or less, or about 0.01 MPa or less.
A variety of types of solid adsorbents are available for separation
of components from a gas flow using temperature swing adsorption
(TSA). During a conventional TSA process, at least one component in
a gas flow can be preferentially adsorbed by the solid adsorbent,
resulting in a stream with a reduced concentration of the adsorbed
component. The adsorbed component can then be desorbed and/or
displaced from the solid adsorbent, optionally to form a stream
having an increased concentration of the adsorbed component.
One of the ongoing challenges with swing adsorption processes is
balancing between the desire to increase the working capacity of
the adsorbent and the desire to reduce the cycle time. For an
idealized process, the working capacity of an adsorbent can be
increased by increasing the severity of the difference between the
conditions during adsorption and desorption of a target component
that is adsorbed out of a gas flow. This can correspond to
increasing the difference in pressure between adsorption and
desorption (typically for PSA), increasing the difference in
temperature between adsorption and desorption (typically for TSA),
or a combination thereof.
In practical application, the amount of pressure and/or temperature
difference between adsorption and desorption can be limited by a
desire to improve total cycle time. Increasing the differential in
pressure and/or temperature between adsorption and desorption can
cause a corresponding increase in the time required for
transitioning between the adsorption and desorption portions of a
cycle. This can include one or both of the transition from
adsorption to desorption or the transition from desorption to
adsorption.
A further complication in swing adsorption processes can be related
to achieving full working capacity and/or achieving full
restoration of the adsorbent monolith to a desired state prior to
the next adsorption step. Equilibrium adsorption isotherms can
describe the potential working capacity that may be achieved during
a full swing adsorption cycle. However, achieving a desired
desorption condition does not guarantee that equilibrium is reached
at that condition. For example, in temperature swing adsorption, it
can be desirable to reduce or minimize the desorption temperature
so long as the temperature still achieves a desired amount of
desorption. This can often correspond to a temperature of less than
about 200.degree. C. At such temperatures, desorption to
equilibrium values may take a long time relative to a cycle time,
as random fluctuations within the temperature ensemble state may be
needed to achieve desorption of individual adsorbed compounds.
The problem with incomplete desorption can be further exacerbated
if other fluids are present in the desorption environment. For
example, one potential option for increasing the rate of
temperature change during a swing adsorption process could be to
use a liquid phase fluid to provide better thermal contact and/or
heat capacity. However, such a fluid can potentially become trapped
in the porous structures found in many adsorbents. Simply
increasing the temperature of the adsorbent monolith to the
desorption temperature may be insufficient to dislodge such fluids
that are within the pores of the adsorbent.
In various aspects, the above difficulties with balancing the
driving force for desorption with the desire for shorter cycle
times can be reduced, mitigated, or minimized by not to operating
the TSA process to the full capacity of the adsorbent bed. In other
words, the TSA process can be used as a concentrator to form a
CO.sub.2-rich stream to be further separated by a second stage
adsorption process. This reduces the heat of adsorption in the TSA
process and also decreases the steam usage required to regenerate
the adsorbent.
Displacement Adsorption/Desorption Processes
Displacement Adsorption/Desorption ("DD") processes employ
gas-solids contactors in which the sorbent is alternately exposed
to the feed gas and to steam wherein the gas and steam are
essentially at the same temperature. In the steaming step the
carbon dioxide adsorbed from the gas is released from the sorbent
by a combination of concentration swing and desorptive
displacement, thereby regenerating the sorbent for re-use. No
external application or removal of heat is used, and the process
operates at essentially constant pressure. The process is notably
identifiable and distinguishable and beneficial as compared to
pressure swing or partial pressure swing separation in that during
the adsorption of CO.sub.2 the bed temperature decreases below the
average bed temperature as determined over the entire cycle and
during CO.sub.2 displacement/desorption the bed temperature
increases above the average. The process is further distinguished
and beneficial as compared to thermal swing separation in that no
external heat is applied and the desorption gas, steam, is
essentially isothermal with the feed gas. The gas-solids contactors
may use moving solid sorbents, or solid sorbents contained in
packed beds or in parallel-channel beds (monoliths). The packed bed
or monoliths can be rotating or stationary. To permit continuous
flow of inlet and outlet streams, multiple beds can be combined
with appropriate valving to switch individual beds between
adsorption and desorption. Such multiple bed arrangements can be
operated to achieve counter-current staging. The water and energy
from the regeneration steam can be recaptured after use and
recycled back into the process.
Some DD regeneration processes use contact with steam to remove the
adsorbed gas from the sorbent. The regeneration mechanism can be by
a combination of concentration swing and desorptive displacement of
the adsorbed gas with steam. The disclosure can further relate to a
method to recycle the steam and recover its energy through a
multi-stage condenser/heat exchangers system. The advantage of this
option is that it increases system efficiency.
DD processes can be used for removal of CO.sub.2 from a combustion
flue gas or natural gas stream or other streams. An advantage is
that the adsorbent can be rapidly regenerated essentially
isothermally with steam and discharge a moist CO.sub.2 stream
wherein the CO.sub.2 concentration is higher than that in the
original feed gas. Another advantage of the sorbent is that it can
be used in an adiabatic reactor design. The sorbent adsorbs water
during regeneration with steam and then desorbs water during
CO.sub.2 adsorption so that the net reactions are exothermic during
steaming and endothermic during adsorption. In this way the system
does not require external thermal management on the adsorber and
regenerator beds. This modest temperature swing is also important
because it thermally assists both adsorption and desorption, again
without the addition of external thermal management.
High process efficiency can be important in order for CO.sub.2
capture to be economical. The regeneration system can be designed
to recycle the steam and recover its energy.
The process can be carried out in a cyclic adsorption/regeneration
cycle and can include various intermediate purges and stream
recycles. Such a process can be performed with co-directional flow
of the feed gas and regeneration steam, but can be preferably
performed with counter-current feed adsorption/steam regeneration
steam flows.
The process can include the steps of passing a gas stream
comprising CO.sub.2 over a sorbent to adsorb the CO.sub.2 to the
sorbent, and then recovering the CO.sub.2 by desorbing the CO.sub.2
from the sorbent. As noted above, and discussed in more detail
below, the adsorption/desorption process can be based on
concentration swing and desorptive displacement. Concentration
swing adsorption (CSA) processes including the adsorption and
desorption steps are governed by change in fugacity of the
adsorbate, in this case, CO.sub.2, in the gas stream, in comparison
to the adsorbent. The adsorbate, in this case CO.sub.2, is adsorbed
when its fugacity is high in the gas stream and low in the
adsorbent. Conversely, it is desorbed when its fugacity is reduced
in the gas stream relative to the amount in the adsorbent. By way
of example, an adsorbent having a high level of CO.sub.2 might
still adsorb additional CO.sub.2 when the gas stream has a
relatively higher fugacity of CO.sub.2 versus the adsorbent. And an
adsorbent having a low level of CO.sub.2 can adsorb CO.sub.2 when
the gas stream has a low fugacity of CO.sub.2 so long as the
relative fugacity of CO.sub.2 in the sorbent is still lower than
the CO.sub.2 in the gas stream. One of ordinary skill in the art
would also recognize that "relative fugacity" does not imply
relative concentration in the absolute value sense, i.e. does not
mean that a 2% adsorbed CO.sub.2 content is necessarily larger than
a 1% CO.sub.2 gas level, because the ability of the gas to retain
CO.sub.2 versus the ability of adsorbent to adsorb additional
CO.sub.2 will be governed by various equilibrium relationships.
DD processes also include desorbing the CO.sub.2 from the sorbent.
This step might also be referred to as a regeneration step because
the sorbent is regenerated for the next passage of a CO.sub.2 gas
stream across the sorbent. The desorption of CO.sub.2 from the
sorbent comprises treating the sorbent with steam. This desorption
step can be driven by a one or more forces. One desorption force is
concentration swing, as with the adsorption step above. The partial
pressure of CO.sub.2 in the incoming steam is nearly zero, and thus
the adsorbed CO.sub.2 can shift to the steam phase. The second
desorption force is desorption by displacement. The water molecules
in the steam can adsorb onto the sorbent and displace the CO.sub.2
from the sorbent.
As an optional step, the processes, methods and systems of the
disclosure can also include one or more purging step, in which a
non-adsorbent gas, i.e. not steam or a CO.sub.2 feed stream, can be
passed across the sorbent. The gas can be any gas known to one or
ordinary skill in the art, such as for example an inert gas or air.
In an embodiment, the purge gas can be a nitrogen stream, an air
stream, or a dry air stream. Alternatively the purge gas can be a
CO.sub.2 feed gas or steam that is recycled into a process step.
The purge step can be conducted at any time. For example, prior to
the passing of the CO.sub.2 feed stream across the sorbent, a purge
gas can be passed to remove residual and adsorbed water vapor. This
purge gas can be run back into the regeneration side in order for
the water vapor to be readsorbed onto the regeneration side. The
purging step can also occur between the adsorption step or steps,
and the desorption or regeneration step or steps. The purge gas can
be non-reactive, but can still optionally remove adsorbed CO.sub.2
from a sorbent based on concentration swing. Thus, in an
embodiment, the purging step can be conducted after adsorption
steps, and can be conducted to remove residual gas prior to
desorption, which can be optionally recycled into the process.
Moreover, the purge step can also be optionally diverted into two
streams: 1) an initial purge stream to remove the first gas, and 2)
a separate purge stream that can contain the initial purified or
desorbed CO.sub.2, which could be optionally captured as part of
the final product stream. Furthermore, in an embodiment, a purging
step can be conducted after the desorption or regeneration step(s)
is complete, thereby optionally removing residual water and/or
steam which can be recycled back into the process. Each purging
step can thereby reduce an excess gas stream which can, for example
lead to a more efficient process or produce a more CO.sub.2
enriched product stream because a final product stream is not
diluted by a preceding gas source. By way of specific example, a
purging step conducted after the initial adsorption can remove
residual, dilute CO.sub.2 feed stream, leading to a more
concentrated CO.sub.2 product stream. The resulting gas stream from
the purging step can be recycled into the system, or split into a
recycle and a product stream.
Additionally, different separations processes are more effective at
different concentrations of adsorbate in a feed. Specifically, TSA
processes are generally more effective at lower adsorbate
concentrations, while DD processes are generally more effective at
higher adsorbate concentration. For example, in FIG. 3 shows graph
of steam usage in moles as a function of CO.sub.2 concentration for
a single stage displacement process. As shown, as CO.sub.2 loading
increases, the amount of steam usage decreases. In other words,
displacement processes have been shown to be more efficient when
there is a higher concentration of CO.sub.2 in the incoming
feed.
Different processes likewise have disadvantages. In DD processes
when CO.sub.2 concentration in the incoming feed is at lower
levels, the amount of steam required to separate the CO.sub.2 to an
acceptable level is cost prohibitive. Regarding TSA processes,
adsorption is exothermic. In many TSA adsorbents, especially in
certain metal organic frameworks (MOFs), the amount of heat
generated when loading the adsorbent to capacity is unacceptable.
McDonald et al. (519 NATURE 303, 307) explain, "Because of the
exothermic nature of all adsorption processes, the incorporation of
labour and material intensive coolant pipes into an adsorbent bed
(a component of the considerable infrastructure cost for carbon
capture) is necessary to maintain isothermal adsorption conditions
. . . . The physical size of adsorption units is dictated, to a
great extent, by the need to provide sufficient contact area
between the coolant and sorbent for effective heat removal."
Examples of Adsorbent Structures
In various aspects, an adsorbent structure can correspond to a
contactor for use in a swing adsorption vessel. More generally, in
this discussion an adsorbent structure can correspond to any type
of structure, either rigid or non-rigid, that includes or
incorporates an adsorbent suitable for adsorption of a gas
component during a swing adsorption process. This can include
conventional contactor adsorbent structures, such as parallel plate
contactors, adsorbent monoliths, and other conventional structures.
This can also include non-rigid structures, such as flexible,
curtain-like, and/or fabric-like adsorbents that may be able to
exhibit larger amplitude fluctuations in position in response to an
induced vibration. Still other adsorbent structures can correspond
to beds of adsorbent particles, either in a conventional adsorbent
bed configuration or in a non-traditional configuration, such as
use of bed of adsorbent particles under trickle flow
conditions.
A variety of contactors corresponding to adsorbent structures are
known, such as the contactors (adsorbent structures) described in
U.S. Patent Application Publication 2008/0282892, the entirety of
which is incorporated herein by reference. For example, FIG. 1
hereof is a representation of a parallel channel contactor of the
present disclosure in which the parallel channels are formed from
laminated sheets containing adsorbent material. Laminates,
laminates of sheets, or laminates of corrugated sheets can be used
in pressure and/or temperature swing adsorption processes.
Laminates of sheets are known in the art and are disclosed in U.S.
patent applications US20060169142 A1 and U.S. Pat. No. 7,094,275
B2. When the adsorbent is coated onto a geometric structure or
components of a geometric structure that are laminated together,
the adsorbent can be applied using any suitable liquid phase
coating techniques. Non-limiting examples of liquid phase coating
techniques that can be used in the practice of the present
disclosure include slurry coating, dip coating, slip coating, spin
coating, hydrothermal film formation and hydrothermal growth. When
the geometric structure is formed from a laminate, the laminate can
be formed from any material to which the adsorbent of the present
disclosure can be coated. The coating can be done before or after
the material is laminated. In all these cases the adsorbent is
coated onto a material that is used for the geometric shape of the
contactor. Non-limiting examples of such materials include glass
fibers, milled glass fiber, glass fiber cloth, fiber glass, fiber
glass scrim, ceramic fibers, metallic woven wire mesh, expanded
metal, embossed metal, surface-treated materials, including
surface-treated metals, metal foil, metal mesh, carbon-fiber,
cellulosic materials, polymeric materials, hollow fibers, metal
foils, heat exchange surfaces, and combinations of these materials.
Coated supports typically have two major opposing surfaces, and one
or both of these surfaces can be coated with the adsorbent
material. When the coated support is comprised of hollow fibers,
the coating extends around the circumference of the fiber. Further
support sheets may be individual, presized sheets, or they may be
made of a continuous sheet of material. The thickness of the
substrate, plus applied adsorbent or other materials (such as
desiccant, catalyst, etc.), typically ranges from about 10
micrometers to about 2000 micrometers, more typically from about
150 micrometers to about 300 micrometers.
In various aspects, the present disclosure eliminates many of the
inefficiencies contained in the prior art as can be seen with
reference to FIG. 1 and FIG. 2. As shown therein, a two stage
adsorbent contactor is provided. Gaseous stream 101 enters the
first stage adsorbent 102 as shown. Gaseous stream 101 can be, for
example, a flue gas from a natural gas or coal-fired power plant.
Such flue gasses generally contain between 3-7 mol. % CO.sub.2 (for
natural gas plants) or between 10-20 mol. % CO.sub.2 (for
coal-fired plants). Such streams are generally between 60.degree.
C. and 90.degree. C. and are at low pressures--i.e. 2 bar or less.
First stage adsorbent 102 is preferably a steam sensitive
adsorbent. Within first stage adsorbent 102, there can be a
plurality of cylindrical or substantially cylindrical rings 105.
Said cylindrical or substantially cylindrical rings 105 contain gas
permeable walls such that gaseous stream 101 is permitted to
permeate different rings 105 within first stage adsorbent 102. The
first stage adsorbent 102 can be comprised of a MOF. Additionally
or alternatively, the first stage adsorbent 102 is disposed
radially about a central axis; wherein the first stage adsorbent
has an interior surface that is a distance x from the central axis
and an exterior surface that is a distance y from the central axis,
wherein y is greater than x, thereby forming a void space between
the central axis and the interior surface of the first stage
adsorbent.
Also provided is second stage adsorbent 103. Second stage adsorbent
103 is preferably steam insensitive. Within second stage adsorbent
103, there can be a plurality of cylindrical or substantially
cylindrical rings 106. Said cylindrical or substantially
cylindrical rings 106 contain gas permeable walls such that a first
CO.sub.2-rich stream is permitted to permeate different rings 106
within second stage adsorbent 103. The second stage adsorbent 103
can comprise a support and a metal compound selected from the group
consisting of alkali or alkaline earth. Additionally or
alternatively, second stage adsorbent 103 is disposed within the
void space of the first stage adsorbent 102 when the first stage
adsorbent 102 is disposed radially about a central axis; wherein
the first stage adsorbent has an interior surface that is a
distance x from the central axis and an exterior surface that is a
distance y from the central axis, wherein y is greater than x,
thereby forming a void space between the central axis and the
interior surface of the first stage adsorbent 102.
FIG. 2 illustrates an example process utilizing the apparatus
described above is illustrated. Gaseous stream 201 enters first
stage adsorbent 202. Gaseous stream 201 is subjected to a TSA
process with first stage adsorbent 202 such that a first
CO.sub.2-lean stream 208 is formed during the adsorption phase,
which is comprised nearly entirely of nitrogen. CO.sub.2 is then
desorbed from first stage adsorbent 202 using a hot purge gas
thereby forming a first CO.sub.2-rich stream 207. In one aspect,
the CO.sub.2 content of the gaseous stream 201 is between 3-20 mol.
%. In another aspect, the CO.sub.2 content of the first
CO.sub.2-rich stream 207 is about 20-35 mol. %. In another aspect,
the TSA process comprises contacting the gaseous stream 201 with
the first stage adsorbent 202 at a first temperature, said first
temperature being less than an adsorption temperature of CO.sub.2
for the first stage adsorbent 202, heating the first stage
adsorbent 202 with a hot purge gas, wherein the hot purge gas is at
a second temperature, said second temperature being greater than a
desorption temperature of CO.sub.2 for the first stage adsorbent
202. In another aspect of the TSA process the hot purge gas
comprises N.sub.2, CO.sub.2, or flare gas, such as methane. In
another aspect of the TSA process, the temperature differential
between the first temperature and the second temperature is less
than 90.degree. C., less than 70.degree. C., less than 50.degree.
C., less than 30.degree. C., or less than 20.degree. C. In another
aspect, the first stage adsorbent 202 is heated by the hot purge
gas by indirect heat exchange.
In another aspect, the method comprises contacting the first
CO.sub.2-rich stream 207 with a second stage adsorbent 203 such
that CO.sub.2 is adsorbed in the second stage adsorbent 203 and a
second CO.sub.2-lean 209 stream is formed. In another aspect, the
method comprises desorbing CO.sub.2 from the second stage adsorbent
thereby forming a second CO.sub.2-rich stream 210; wherein the
second CO.sub.2-rich stream 210 has a higher CO.sub.2 concentration
by mol. % than the first CO.sub.2-rich stream 207.
As shown in FIG. 2, the contacting the first CO.sub.2-rich stream
207 and the desorbing CO.sub.2 from the second stage adsorbent 203
steps are performed using a displacement process, wherein the
displacement process comprises, contacting the first CO.sub.2-rich
stream 207 with the second stage adsorbent 203 such that CO.sub.2
is adsorbed into the second stage adsorbent 203; and contacting the
second stage adsorbent 203 with steam such that CO.sub.2 is
desorbed from the second stage adsorbent 203. In another aspect,
CO.sub.2 is desorbed from the second stage adsorbent 203 via one or
both of concentration swing and displacement desorption. In another
aspect, the displacement process is conducted at an initial
temperature; wherein the initial temperature does not vary more
than 10.degree. C. during the contacting the first CO.sub.2-rich
stream with the second stage adsorbent 203 and the contacting the
second stage adsorbent 203 with steam steps.
In another aspect, the temperature swing process and displacement
process described above are used as the first and second stage
adsorption/desorption processes, respectively. In another aspect,
the ratio of steam usage in moles to CO.sub.2 recovered in moles is
less than 3. In another aspect, the heat of condensation from the
CO.sub.2 that is desorbed from the second stage adsorbent is used
to heat the gaseous stream.
With reference to FIG. 1, it is to be understood that the flow path
of the various feed and product streams disclosed herein, such as
those depicted in as product streams 104, and the associated
headers, valve manipulations, etc. would be readily recognizable to
one of ordinary skill in the art. Accordingly, such mechanisms are
not shown in the figures for simplicity.
Additional Embodiments
Additionally or alternately, the present disclosure can include one
or more of the following embodiments.
Embodiment 1
An adsorbent contactor for separation of CO.sub.2 from a gaseous
stream, comprising a first stage adsorbent, said first stage
adsorbent being steam sensitive; and a second stage adsorbent, said
second stage adsorbent being steam insensitive.
Embodiment 2
The adsorbent contactor of embodiment 1, wherein the first stage
adsorbent comprises a metal organic framework.
Embodiment 3
The adsorbent contactor of embodiment 1 or 2, wherein the second
stage adsorbent comprises a support and a metal compound selected
from the group consisting of alkali or alkaline earth.
Embodiment 4
The adsorbent contactor of any of the previous embodiments, wherein
the first stage adsorbent is disposed radially about a central
axis; wherein the first stage adsorbent has an interior surface
that is a distance x from the central axis and an exterior surface
that is a distance y from the central axis, wherein y is greater
than x, thereby forming a void space between the central axis and
the interior surface of the first stage adsorbent.
Embodiment 5
The adsorbent contactor of embodiment 4, wherein the second stage
adsorbent is disposed within the void space of the first stage
adsorbent.
Embodiment 6
The adsorbent contactor of any of the previous embodiments, wherein
the first stage adsorbent and the second stage adsorbents comprise
a plurality of cylindrical or substantially cylindrical adsorbent
beds, wherein the walls of the plurality of cylindrical or
substantially cylindrical adsorbent beds are gas permeable.
Embodiment 7
The adsorbent contactor of any of the previous embodiments, wherein
the first stage adsorbent comprises a metal organic framework and
the second stage adsorbent comprises a support and a metal compound
selected from the group consisting of alkali or alkaline earth.
Embodiment 8
A method for separation of CO.sub.2 from a gaseous stream,
comprising contacting the gaseous stream with a first stage steam
sensitive adsorbent such that CO.sub.2 is adsorbed into the first
stage adsorbent and a first CO.sub.2-lean stream is formed;
desorbing CO.sub.2 from the first stage adsorbent thereby forming a
first CO.sub.2-rich stream; contacting the first CO.sub.2-rich
stream with a second stage steam insensitive adsorbent such that
CO.sub.2 is adsorbed in the second stage adsorbent and a second
CO.sub.2-lean stream is formed; and desorbing CO.sub.2 from the
second stage adsorbent thereby forming a second CO.sub.2-rich
stream; wherein the second CO.sub.2-rich stream has a higher
CO.sub.2 concentration by mol. % than the first CO.sub.2-rich
stream.
Embodiment 9
The method of embodiment 8, wherein the first stage adsorbent
consists of a metal organic framework.
Embodiment 10
The method of embodiment 8 or 9, wherein the second stage adsorbent
comprises a support and a metal compound selected from the group
consisting of alkali or alkaline earth.
Embodiment 11
The method of any of embodiments 8-10, wherein the contacting the
gaseous stream and the desorbing CO.sub.2 from the first stage
adsorbent steps are performed using a temperature swing
process.
Embodiment 12
The method of any of embodiments 8-11, wherein the contacting the
first CO.sub.2-rich stream and the desorbing CO.sub.2 from the
second stage adsorbent steps are performed using a displacement
process.
Embodiment 13
The method of any of embodiments 8-12, wherein the pressure of the
gaseous stream is less than 2 bar.
Embodiment 14
The method of any of embodiments 8-13, wherein the temperature of
the gaseous stream is between about 60.degree. C. and 90.degree.
C.
Embodiment 15
The method of any of embodiments 8-14, wherein the temperature
swing process comprises, contacting the gaseous stream with the
first stage adsorbent at a first temperature, said first
temperature being less than an adsorption temperature of CO.sub.2
for the first stage adsorbent, heating the first stage adsorbent
with a hot purge gas, wherein the hot purge gas is at a second
temperature, said second temperature being greater than a
desorption temperature of CO.sub.2 for the first stage
adsorbent.
Embodiment 16
The method of embodiment 15, wherein the hot purge gas comprises
N.sub.2.
Embodiment 17
The method of embodiments 15 or 16, wherein the hot purge gas
comprises N.sub.2 and CO.sub.2.
Embodiment 18
The method of any of embodiments 15-17, wherein the hot purge gas
comprises flare gas, such as methane.
Embodiment 19
The method of any of embodiments 15-18, wherein the first stage
adsorbent is heated by the hot purge gas by indirect heat
exchange.
Embodiment 20
The method of embodiment 15, wherein the temperature differential
between the first temperature and the second temperature is less
than 90.degree. C.
Embodiment 21
The method of embodiment 15, wherein the temperature differential
between the first temperature and the second temperature is less
than 70.degree. C.
Embodiment 22
The method of embodiment 15, wherein the temperature differential
between the first temperature and the second temperature is less
than 50.degree. C.
Embodiment 23
The method of embodiment 15, wherein the temperature differential
between the first temperature and the second temperature is less
than 30.degree. C.
Embodiment 24
The method of embodiment 12, wherein the displacement process
comprises, contacting the first CO.sub.2-rich stream with the
second stage adsorbent such that CO.sub.2 is adsorbed into the
second stage adsorbent; and contacting the second stage adsorbent
with steam such that CO.sub.2 is desorbed from the second stage
adsorbent.
Embodiment 25
The method of any of embodiments 12-24, wherein CO.sub.2 is
desorbed from the second stage adsorbent via one or both of
concentration swing and displacement desorption.
Embodiment 26
The method of any of embodiments 12-24, wherein the displacement
process is conducted at an initial temperature; wherein the initial
temperature does not vary more than 10.degree. C. during the
contacting the first CO.sub.2-rich stream with the second stage
adsorbent and the contacting the second stage adsorbent with steam
steps.
Embodiment 27
The method of embodiment 11, wherein the contacting the first
CO.sub.2-rich stream and the desorbing CO.sub.2 from the second
stage adsorbent steps are performed using a displacement process;
wherein the displacement process comprises, contacting the first
CO.sub.2-rich stream with the second stage adsorbent such that
CO.sub.2 is adsorbed into the second stage adsorbent; contacting
the second stage adsorbent with steam such that CO.sub.2 is
desorbed from the second stage adsorbent.
Embodiment 28
The method of any of embodiments 8-27, wherein the steam usage in
moles to CO.sub.2 desorbed in moles ratios is less than 3.
Embodiment 29
The method of any of embodiments 8-28, wherein the first the first
stage adsorbent is disposed radially about a central axis; wherein
the first stage adsorbent has an interior surface that is a
distance x from the central axis and an exterior surface that is a
distance y from the central axis, wherein y is greater than x,
thereby forming a void space between the central axis and the
interior surface of the first stage adsorbent.
Embodiment 30
The method of any of embodiments 8-29, wherein the second stage
adsorbent is disposed within the void space of the second stage
adsorbent.
Embodiment 31
The method of any of embodiments 8-30, wherein the heat of
condensation from the CO.sub.2 that is desorbed from the second
stage adsorbent is used to heat the gaseous stream.
Embodiment 32
The method of any of embodiments 8-31, wherein the CO.sub.2 content
in the gaseous stream is about 3-10 mol. %.
Embodiment 33
The method of any of embodiments 8-32, wherein the CO.sub.2 content
in the first CO.sub.2-rich stream is about 20-35 mol. %.
Embodiment 34
A system for separation of CO.sub.2 from a gaseous stream,
comprising; a first stage adsorbent, said first stage adsorbent
being steam sensitive; wherein said first adsorbent is subject to a
temperature swing process, said temperature swing process
comprising, contacting the gaseous stream with the first stage
adsorbent at a first temperature, said first temperature being less
than an adsorption temperature of CO.sub.2 for the first stage
adsorbent, heating the first stage adsorbent with a hot purge gas,
wherein the hot purge gas is at a second temperature, said second
temperature being greater than a desorption temperature of CO.sub.2
for the first stage adsorbent, thereby forming a first
CO.sub.2-rich stream and a first CO.sub.2-lean stream; a second
stage adsorbent, said second stage adsorbent being steam
insensitive; wherein said second stage adsorbent is subject to a
displacement process, said displacement process comprising,
contacting the first CO.sub.2-rich stream with the second stage
adsorbent such that CO.sub.2 is adsorbed into the second stage
adsorbent; contacting the second stage adsorbent with steam such
that CO.sub.2 is desorbed from the second stage adsorbent, thereby
forming a second CO.sub.2-rich stream and a second CO.sub.2-lean
stream; wherein the second CO.sub.2-rich stream has a higher
CO.sub.2 concentration by mol. % than the first CO.sub.2-rich
stream.
Embodiment 35
The system of embodiment 34, wherein the first stage adsorbent is
disposed radially about a central axis; wherein the first stage
adsorbent has an interior surface that is a distance x from the
central axis and an exterior surface that is a distance y from the
central axis, wherein y is greater than x, thereby forming a void
space between the central axis and the interior surface of the
first stage adsorbent.
Embodiment 36
The system of embodiment 34 and 35, wherein the second stage
adsorbent is disposed within the void space of the first stage
adsorbent.
Embodiment 37
The system any of embodiments 34-36, wherein the first stage
adsorbent and the second stage adsorbents comprise a plurality of
cylindrical or substantially cylindrical adsorbent beds, wherein
the walls of the plurality of cylindrical or substantially
cylindrical adsorbent beds are gas permeable.
Although the present disclosure has been described in terms of
specific embodiments, it is not so limited. Suitable
alterations/modifications for operation under specific conditions
should be apparent to those skilled in the art. It is therefore
intended that the following claims be interpreted as covering all
such alterations/modifications as fall within the true spirit/scope
of the disclosure.
Examples of CO.sub.2 Concentration in First Stage Adsorben
The following calculations are based on sophisticated modeling
techniques, which mimic CO.sub.2 concentration that would occur
during a first stage adsorption process of the present
disclosure.
Example 1
A high capacity MOF adsorbent was subjected to a thermal swing
cycle which consisted of the consecutive steps of feeding a bed of
said adsorbent with dimensions 1 sq. m cross-section and 2 m
length, with 0.045 kg/s of flue gas containing 6% CO2 at 80.degree.
C. for 150 s, regenerating with countercurrent hot N.sub.2 at 120
deg C. for 180 s followed by cooling with countercurrent N.sub.2 at
80 deg C. for 60 s. The process is made continuous by using 3 beds
that are run out of phase with each other, such that one bed is one
feed while the other two beds are being either regenerated or
cooled. Computer simulations of the cyclic process, using
properties of the specified MOF adsorbent show that a combined
product from both heating and cooling steps containing 22.7%
CO.sub.2 is produced. Simultaneously a purified N.sub.2 product (or
green flue gas) is produced containing 99.9% N.sub.2. The recovery
of the CO.sub.2 is .about.98.3% from this first stage of the hybrid
contactor.
TABLE-US-00001 Feed Heat Cool N.sub.2 product CO.sub.2 product
Moles 232.97 38.53 10.71 221.10 60.63 CO.sub.2 fraction 0.060 0.001
0.000 0.001 0.227 N.sub.2 fraction 0.940 0.999 1.000 0.999
0.773
Example 2
A high capacity MOF adsorbent was subjected to a thermal swing
cycle which consisted of the consecutive steps of feeding a bed of
said adsorbent with dimensions 1 sq. m cross-section and 2 m
length, with 0.04 kg/s of flue gas containing 6% CO.sub.2 at 70 deg
C. for 180 s, regenerating with countercurrent hot N.sub.2 at 110
deg C. for 240 s followed by cooling with countercurrent N.sub.2 at
70 deg C. for 120 s. The process is made continuous by using 3 beds
that are run out of phase with each other, such that one bed is one
feed while the other two beds are being either regenerated or
cooled. Computer simulations of the cyclic process, using
properties of the specified MOF adsorbent show that a combined
product from both heating and cooling steps containing 22.2%
CO.sub.2 is produced. Simultaneously a purified N.sub.2 product (or
green flue gas) is produced containing 99.9% N.sub.2. The recovery
of the CO.sub.2 is .about.99.9% from this first stage of the hybrid
contactor.
TABLE-US-00002 Feed Heat Cool N.sub.2 product CO.sub.2 product
Moles 248.51 34.25 21.42 236.22 67.68 CO.sub.2 fraction 0.060 0.001
0.000 0.0004 0.222 N.sub.2 fraction 0.940 0.999 1.000 0.999
0.778
Example 3
A high capacity MOF adsorbent was subjected to a thermal swing
cycle which consisted of the consecutive steps of feeding a bed of
said adsorbent with dimensions 1 sq. m cross-section and 2 m
length, with 0.045 kg/s of flue gas containing 6% CO.sub.2 at 80
deg C. for 150 s, regenerating with countercurrent hot N.sub.2 at
120 deg C. for 240 s followed by cooling with countercurrent
N.sub.2 at 80 deg C. for 60 s. The process is made continuous by
using 3 beds that are run out of phase with each other, such that
one bed is one feed while the other two beds are being either
regenerated or cooled. Computer simulations of the cyclic process,
using properties of the specified MOF adsorbent show that a
combined product from both heating and cooling steps containing
22.2% CO.sub.2 is produced. Simultaneously a purified N2 product
(or green flue gas) is produced containing 99.8% N.sub.2. The
recovery of the CO.sub.2 is .about.97.1% from this first stage of
the hybrid contactor.
TABLE-US-00003 Feed Heat Cool N.sub.2 product CO.sub.2 product
Moles 232.97 38.53 10.70 220.97 61.23 CO.sub.2 fraction 0.060 0.001
0.001 0.0018 0.222 N.sub.2 fraction 0.940 0.999 0.999 0.998
0.778
Example 4
A lower capacity MOF adsorbent was subjected to a thermal swing
cycle which consisted of the consecutive steps of feeding a bed of
said adsorbent with dimensions 1 sq. m cross-section and 3 m
length, with 0.02 kg/s of flue gas containing 6% CO.sub.2 at 80 deg
C. for 180 s, regenerating with concurrent hot CO.sub.2/N.sub.2
mixture at 100 deg C. for 90 s followed by concurrent hot
CO.sub.2/N.sub.2 mixture at 130 deg C. for 90 s, subsequently
conducting countercurrent pure N.sub.2 at 130 deg C. for 90 s,
followed by cooling with countercurrent N.sub.2 for 90 s. The
process is made continuous by using 3 beds that are run out of
phase with each other, such that one bed is one feed while the
other two beds are being either regenerated or cooled. Computer
simulations of the cyclic process, using properties of the
specified lower capacity MOF adsorbent (ref. 2) show that a
combined product from all staged the three staged heating steps and
the cooling step contains 33.4% CO.sub.2. Simultaneously a purified
N.sub.2 product (or green flue gas) is produced containing 99.4%
N.sub.2. The recovery of the CO.sub.2 is .about.86.5% from this
first stage of the hybrid contactor after accounting for the
amounts of 50% CO.sub.2/N.sub.2 streams used in the staged heating
steps which are recycled into the process.
TABLE-US-00004 N.sub.2 CO.sub.2 Feed Heat-1 Heat-2 Heat-3 Cool
product product Moles 124.25 24.99 24.99 64.25 32.13 176.32 94.13
CO.sub.2 fraction 0.06 0.5 0.5 0.000 0.000 0.006 0.334 N.sub.2
fraction 0.94 0.5 0.5 1.000 1.000 0.994 0.666
Example 5
A high capacity MOF adsorbent was subjected to a thermal swing
cycle which consisted of the consecutive steps of feeding a bed of
said adsorbent with dimensions 1 sq. m cross-section and 2.5 m
length, with 0.03 kg/s of flue gas containing 14% CO.sub.2 at 100
deg C. for 60 s, regenerating with countercurrent hot N.sub.2 at
120 deg C. for 120 s followed by cooling with countercurrent
N.sub.2 at 100 deg C. for 60 s. The process is made continuous by
using 4 beds that are run out of phase with each other, such that
one bed is one feed while the other two beds are being either
regenerated or cooled. Computer simulations of the cyclic process,
using properties of the specified MOF adsorbent show that a
combined product from both heating and cooling steps containing
20.3% CO.sub.2 is produced. Simultaneously a purified N.sub.2
product (or green flue gas) is produced containing 99.93% N.sub.2.
The recovery of the CO.sub.2 is .about.98.3% from this first stage
of the hybrid contactor.
TABLE-US-00005 Feed Heat Cool N.sub.2 product CO.sub.2 product
Moles 59.50 25.69 10.70 54.70 40.34 CO.sub.2 fraction 0.140 0.001
0.001 0.0007 0.203 N.sub.2 fraction 0.860 0.999 0.999 0.9993
0.797
* * * * *